Antenna system with variable directional characteristic



ANTENNA SYSTEM WITH VARIABLE DIRECTIONAL CHARACTERISTIC Filed Nov. 10, 1943 July 29, 1952 L. w. ALVAREZ Luis w A| vAREz l l TRANSMITT ER RECEIVER July 29, 1952 w. ALVAREZ ANTENNA SYSTEM WITH VARIABLE DIRECTIONAL CHARACTERISTIC Filed NOV. 10, 1943 5 Sheets-Sheet 2 m9, DRIVING MEcHANlsM RECEIVER TRANSMITTER SWW/Wto@ LU IS W- ALVAR EZ July 29, 1952 1 w. ALVAREZ l 2,605,413

ANTENNA SYSTEM WITH VARIABLEA DIRECTIONAL CHARACTERISTIC Filed Nov. 10, 194DI 5 Sheets-Sheet 3 Syvum/vw@ LUIS W ALVAREZ @M ff-fmw/w L. W. ALVAREZ July 29, 1952 5 Sheets-Sheet 4 Filed Nov. l0, 1943 S/A I y @VK QQ 0/ f f E IIIHIIIIIIIIIIIHIIIIIIIIIIHIIQ/,M

/4 Mii-EET- (IIIIHII S NDING WAVE ETECTOR /56 RECEIVER TRANSLATIN /6/ DEvvlcE 3M LUIS W-ALVAR INDICATOR MooULAToR @www July 29, 1952 L. w. ALVAREZ ANTENNA SYSTEM WITH VARIABLE DIRECTIONAL CHARACTERISTIC Filed Nov. 10, 1945 5 Sheegs-Sheet 5 gmc/who@ LUIS WALVAREZ Err/7 iatented .ul'y 29, .1952

ANTENNA SYSTEM W'I'r'H DIRECTIONAL CHARACTERISTIC Luis W. Alvarez, Belmont, Mass., assigner, by

mesne assignments, to the United States of America as represented bythe Secretary ofthe Nav-y Y Application November 10, 1943,'SerialNo. 509,790'

This invention relates to directive antenna systems for transmission and reception of high-frequency radio waves particularly to directive antenna systems with variable directional characteris'tcs in at least one plane which characteristics may be adjusted or variedin a relatively continuous manner independently of the physical location in space of the structure.

I have :found that a hollow pipe wave guide is particularly useful for feeding phased radiating and receiving antenna arrays adapted to have their directional characteristics changed by a change of' phasing in the feed line, because such change-of phasing can be accomplished in a relatively simp-le manner by changing the wave length of the oscillations in the hollow pipe waveguide. The simplest forniof phased radiating array fed by ahollow pipe wave guide is'the provision of a 'series` of slots or apertures in the wall of the wave guide spacedby a suitable distance, normally in the neighborhood of the Wave length of the oscillations in the; wave guide. 'Because the wave length of the oscillations in the waveguide is'normally greater than that in unconfined space, the radiation from an arrangement such asV that just mentioned will take place in several sharply de- Vlined directions, corresponding tothe diierent orders'of spectra formed b'ya diffraction grating. In order that only the central vbeam may be radiated it is necessary thatthe slots in the wave Yguide should be separated by a distance less than the wave lengths in Vunconlned Vair or else that the'radiating elements Should themselves have directive characteristics sharp enough to suppress the eXtra order beams. The former alternative may -be realized by introducing dielectric material in the wave guide which has the effect of :shortening the wave length in the wave guide, .and by some other Vsimilar methods. Such arrangements, however, often make it diflicult to Aprovide the desirable variation of the wave length :in Vthe wave guide for varying the orientation of :theradiated beam.

By .the present invention I have .provided -for .close spacing of wave-guide-fed radiating ele- '.ments by providing radiating elements alternate '.by a half-wave length in the guide, which half- `:wave length` is usually shorter than the full Wave lengthin aireven for air-lled hollow pipe wave guides. Since'the, hollow pipe waveguide may 'then be airllled, it then becomes'relatively sim- 2 ple to change the wave length of the wavestliere- 1n.

Thesimplest form-ofradiating elements readily amenable to a'reversal of polarity inthe-fee'dis a dipole fed by ashorttwo-conductor transmission line from the waveguide which provides Ythe power forthe array and also provides vthe-phasing. VI- have worked out many formsof readily-'variable phased arrays employingfdipoles mounted upon wave guides and constituting various forms-ofthe present invention which are described below and illustrated in the attached drawings, in which-'1 Fig. l is a perspective view illustratingthegeneral principles ofA the construction and opera-tion of antenna systems in accordance withthef-present invention;

Fig. 1A is a perspectiveview, partyfbroken-away, illustrating another method-of obtainingI asingle Ybroadside beam from an air-*lledwaveguideby introducing a phase reversalat alternateI radiatingelements;

Fig. 2 is a cross section illustrating angi'mpro've'd form of dipole antenna for use in anarrangement such asfthat of Fig. 1 and Figf` 27A 4gives a perspective View of the same, omitting th asso,- ciated hollow pipewave-,guide Fig. 3 shows, in elevation, an antennasystem according' to the present invention vincluding means for continuously varying the phasing of the' array; g

` illustrating another form of reflector adapted for use in asystem similar` to that shownin'Fig. .4;

Fig. 6 is aperspective view, partly brokenaway, of an antenna system in accordance with the present invention illustrating another method of varying. the .directional Afcharacteristics without physically varying the physical positionoithe radiating elements;

Fig. 7 shows, in cross section, stillanother'form of thepresent invention;

Fig. 8 is a plan View, partially diagrammatic, of Van'g'irnproved form'of the presentA invention" for relatively Wide angle variation in theorientation of tnedirective maximum oftheantenna system;

Fig. 9 shows, partly morose-section, afor'mof the invention adaptedefor variationiof thegorientation of the directiveimaximum-of'theantehna system with rapidityiover ana-ngle offabout- 10;

' Fig. 10 is al perspective view, partly brkenaway,

' use in connection with circularly polarized radiation;

' Fig. 12 is a perspective view, partly broken away, illustrating a modified form; of the present A invention employing radiating elements of the type shown in Fig. 1l;

Fig. 13 is an end View of an apparatus such as that shown in part in Fig. 12 arranged to cooperate with a special type of auxiliary reflector;

Fig. 14 is a diagram illustrating the scanning characteristics of forms of the invention such as those illustrated in Figs. 2 and 7;

Fig. 15 is a plan view of another possible form of apparatus in accordance with the present invention, and

Fig. 16 is a perspective view, partly broken away, illustrating still another method of obtaining a single broadside beam from an air-iilled wave guide lay-introducing a phase reversal at alternate radiating elements.

Figs. 17 and 18 illustrate, respectively in perspective and in elevation, still another arrangement for obtaining a single broadside beam from an air-filled feed Wave guide by introducing an additional relative phase reversal at alternate radiating elements; y

Figs. 19 and 20 are kcross-sectional views illustrating arrangements for concentrating radiation somewhat with respect to directions in a plane perpendicular to the axis of the antenna system; y Figs. 21 and v22 illustrate an arrangement for matching a scanning antenna according to this invention to a wave guide leading to a transmitting and receiving system, Fig. 21 being a front view,` partly broken away, and Fig. 22 being a cross-section," and l Figs. 23 and 24 illustrate another arrangement for matching a scanning antennar according to this invention to a wave guide leading to a transmitting and receiving system, Fig. 23 being Va back view, partly broken off, and Fig. A24 being a crosssection along the line 24-24 of Fig. 23.

One object of this invention is to provide directive antenna systems having more sharply directive properties in at least one plane thanthe more conventional antenna system used for very short waves. Another object of the present invention is to provide highly directive antenna systems the orientation of the directive patterns of which may be continually varied without actual motion of the radiating elements or of any associated reflectors. Other objects of the invention will be apparent from the reading of this specification.

Fig. 1 shows a rectangular wave guide pipe I fed with electromagnetic oscillations of very high frequency-for example about 3000 megacycles per second-produced by a generating device 2' which may be a magnetron type of transmitting tube operated intermittently by means (not shown) to produce short-duration high-intensity pulses of energy. A magnet for producing the magnetic field required by the magnetron tube is shown at 3. VThe hollow pipe wave guide I is excited by the generating device! through a coaxial conductor transmission line 4 the central conductor of which passes centrally through the wave guide I parallel toits shorter cross-sectional dimension, so that the TELO mode of oscillation may readily be excited. Beyond the wave guide I the transmission line ll is short-circuited at a suitable location by a terminal plug 5 and likewise the wave guide I is short-circuited by the wall 6 at a suitable location on one side of the transmission line Il.

The wave guide I is adapted to transmit the TEo,1 mode of oscillation excited by the transmission line t without substantial interference arising from the presence of other modes. Such oper- .ation is obtained by suitably arranging the dimension of -the wave guide I. For this purpose the cross section of the wave guide I is preferably approximately 0.3 by 0.7 wave lengths, referring to the free-space wave length of oscillations of the frequency in question. As is well known, the wave length of the oscillation in the pipe I will be greater than the said free-space wave length. The part of the pipe I immediately to the left of the transmission line 4 is shown in dotted lines in order to indicate that the pipe may be, and preferably is, a great deal longer than can be conveniently illustrated in Fig. l. If it is desired to operate the apparatus of Fig. l for receiving as well as for transmitting, a branch wave guide may be connected with the pipe I near its right-hand end, preferably on the back side, for connection of the pipe I to a receiving apparatus, said branch pipe being preferably provided with a protective electrical breakdown device adapted to short-circuit the branch pipe while the generating device 2 is in operation. Such short circuit may, in accordance with known principles, be made to occur in such a location that it does not interfere with the transmission of electromagnetic waves along the pipe I.

At regular intervals along the length of the pipe I, said intervals beingless than the said free-space wave length of oscillations of the frequency in question, small branch wave guides "I, of the coaxial-conductor type, are provided on one of the broader walls of the pipe I. The coaxial-conductor transmission lines 'I are coupled to the wave guide I by the projection of the inner conductors of the respective coaxial-conductor guides into the hollow pipe wave guide I. Since this projection of the said inner conductors is in a .direction parallel with the electric vector of the TELO Wave in the pipe I, the coaxial-conductor guides Will be excited by the wave in the pipe I and the relative phase in which the several coaxial conductor guides are excited will depend upon the phase shift of the electrical vector of the TE1,n wave along the length of the Wave guide I, in other Words upon the electrical length of the intervening portions of the wave guide I. Thus if the spacing .between centers of adjacent coaxial conductor guides I is equal to a half-wave length of the TEL() Wave in the guide I, the said coaxial conductor guides] will be excited exactly in phase Opposition.

Each of the coaxial conductor guides 'l terminates in a dipole antenna. As shown in Fig. 1 at 8, 9, IIJ and II, these dipole antennas are each oriented parallel to the broader cross-sectional dimension of the wave guide I and all of these dipoles are at the same distance from the nearer broad wall of the wave guide I, to which they are parallel. If desired, the dipole may be oriented parallel to the longitudinal axis of the wave guide (e. g. Fig. 15), or at 45, etc., but they should in each case be substantially parallel to each other.

The distance between the dipoles and the outer surface of the wave-guide wall is preferably made tov be such that reflection of energy from the forcement of vradiationffrom-the dipoles the` directions away fro'mthe wave guide nearfthe plane vpassing through Athe axisoffthe array and perpendicular to the reflecting wave-guide wall.

cidedly'unfavorable.- Actually, the gain* of the individual antennaelements in the forward di-v rection is not of -greatf'importancefsince the length'of the array provides suchag-reat dealY of ganwhile providing the desiredresolution 1 The dipole antennas 8i' 9, VIll and IIY and'other dipole antennas (not shown) that may be located uponthe portion ofthe wave guide pipe IA showny in dotted lines, are not oriented entirely alike, however, for alternate dipoles are effectively'reversed, which is to say that while the upper arm of the dipoles 8 and in lis connected to the central conductor of the correspondingr coaxial structure I and the lowerarms of the dipoles 8 and Ill are connectedto the outer conductor of the structures 1, in the case of the dipoles 9 and II it is the lower arm that is connected to the central. conductor ofA the corresponding structure I and the upper arm of the dipoleY that is connected to the outer conductor ofthe structure 1. Thus, if for instance the structures I and consequently the associated dipoles, are spaced Aby one-half ofV the wave length of the oscillations in the wave guide VI', then, although th'ealternate members ofthe series of coaxial structures 'I will be driven in relative phasejopposition, the alter` nate reversals of the dipole connection will compensate for such phase opposition and all the dipoles will be-excited in phase. In consequence a directive beam of radiation greatly concentrated in a plane perpendicular to theaxis of the waveguide I.will be formed. A similar directional characteristic will' be `obtained for reception purposes. If the length of the array'is large, the concentration of the beam in such plane lwill be very great, it "being entirely practical to obtain a beam having a width of one-half a degree between half-power. points with antenna structures ofv reasonable proportions. Within the said plane in which the vbeam tends to be concentrated as aforesaid; the radiation is fairlybroadly distributed in direction. The reflecting effect of the wall of the wave guide I does provide some directivity, the half-power width of the beam in av plane perpendicular to the Vairis of. the wave guide I being on this account about 60, usually. Ihegbeam may be further concentrated in this plane by the use of reflectors aslshown in Figs.- 4 and or by distributing the dipole radiators in two directions as shown in Fig. 10. Some concentration of this'sort may also be achieved by using reflecting strips mounted on the feed wave guide, as shown in Figs. 19 and 20 and further described below.

. Ifthespacingl between centerspof the coaxial structures 'I is not A180 electrical degrees (a half-v wavey length of the oscillations inthe wave guide I) but some other value, preferablyybetween aboutl: 14o-land 22095; .the reversal of# alternate 'impregnated with graphite.

dipole connections still cooperates inthe :frma-J Y tion -of asingle sharply defined beam by causing successive dipolesl to have a progressive phase shift so that a beamis radiated at anangle to the axis of the wave guide I which is determined in accordance with well-known principles by the phase difference between successive dipoles.

In the arrangement of Fig. 1 energy proceeding to the left in the wave guide pipe I is diminished by amounts of energy abstracted' by the coaxial structures 1, so that only a small amount, which may be 5 per cent or 10 per cent, continues to travel down the pipe I beyond the last of the coaxial structures 1. Although this remaining amount of energy is usually relatively-small, it should nevertheless notbe allowed Vto'build up standing waves in the wave guide I as a result of reflection from the left-hand end of the saidV waveguide if such reflection elect can be prevented. Consequently the left-hand end of the wave guide I is preferablyilled with a suitableY absorbing material, which may be cotton gauze The location of the absorbing material is indicatedr by the dotted line at I2. The absorbing material is preferably chosen in accordance with well-known principles to provide a very small amount of reflection, if any. Instead of an absorbing material filling the whole end portion of the wave guide I, a suitable resistory interposed across the central part of the wave guide I and parallel to the narrow crosssectional dimension thereof may be employed.V

ATheV coaxial structures I which support and feed the dipoles 8, 9, I0, II, and so on, may be arranged any of a number of ways. In the form of the invention illustrated in Fig. l the space between the two coaxial conductors of the said structures is preferably filled with a solid dielectric material such as polystyrene in .orderf to support the inner conductor relative to the outer conductor. Such material tends to shorten the wave length inside the' coaxial conductor structure, but this is not important since an equal effect will take place in each of the structures 1. In the form of apparatus shown in Fig. 1 the ends of the structures l which terminate in the dipoles 8, 9, I0, Il and so on are obliquely terminated, in order to provide clearance between the dipole arm connected to the inner coaxial conductor and the nearby portion of the outer coaxial conductor, so that the dipole arms of each dipole may be properly aligned with each other.

The center conductor of the coaxial structures, instead of being supported as in Fig. 1 by dielectric material, may be supported by continuing the coaxial structures beyond the dipoles in such a manner as to provide a resonant lshort-circuited stub-support, the necessary aperture being made Vin the outer conductor for the passage of the dipole arm connected to the inner conductor. Still further modification of the manner of excitingthe dipoleis possible with improvement in result and I have shown in Figs. 2, 2A and 7 certain preferred forms'of structures for exciting dipoles in apparatus of the present invention, which are described in detail below.

Fig. 1A shows another method of obtaining the phase reversal required for obtaining a single narn row beam from a series of spaced radiators fed from an air-filled hollow pipe wave guide. A portion of a rectangular hollow pipe wave guide is shown at I5 which is adapted to be excited in the TEo,1 mode. The radiating elements are in this case simplyslots I6 in. one of the narrower walls kof Vthe wave guide. The centers of the slots are spaced preferably between 140 andv 2,20 electrical degrees apart. Alternate slots are covered lby plates of rutile, such as the plate |-1,- in which the wavelength of the radiation is very much shorter than the wave length of such radiation in air. The plate |1 is of such thickness that the phase of the radiation is retarded 180 with respect to the phase that would have been obtained had the plate been absent. For the very high frequencies here concerned the rutile plate|1 should have a thickness of the order of magnitude of 6 mm. The Vplate l1 may be conveniently cemented-to the wall of the wave guide I5. In the arrangement illustrated in Fig. 1A it is possible that the radiation resistance of the covered slot may be somewhat diiferent from that of the uncovered slot, so that'the suppression of undesired side beams may not be complete. To some extent itis possible that this may be compensated for by providing structures in the wave guide I5, between the slot locations, which have theeffect of shunt reactances. Such arrangements, in accordance with known principles, may serve to equalize the energy transfer through the two different type of slots. This phase reversal by means of a suitable dielectric plate may also be used with other forms of slot arrays associated with wave guides, such'as arrays of transverse slots cutin the broad side of a rectangular pipe, and soon.Y The slots in each case are located so as to intercept oscillatory currents associated with the transmitted oscillations. Transverse slot arrays modified as in Fig. 1 may also be constructed with a coaxial-conductor wave guide.

Fig. 16 shows another arrangement for providing a relative phase reversal in connection with the radiation from slots cut in a hollow pipe wave guide. In Fig. 16, the slots |10, |1l are cut in the broad sideof a rectangular wave guide, preferably in the center portion thereof. Normally no radiation, or very little radiation, will occur from slots so located, but screws |12 and |13 are inserted into the wave guide to distort the eld within the wave guide so that lan electric field will appear across the slot. The screw |12 is on one side of the slot |10, whereas the screw |13 is on the other side of the slot |1|, so that the field distortion is geometrically in opposite directions for successive slots, thereby providing the desired phase reversal. I

Still another method for providing a relative phase reversal in connection with radiation from spaced locations along a wave guide is shown in Figs. 17 and 18. The radiation in this case takes place from short cylindrical branch wave guides |15, |16 and |11 and so on, supported on'one of the broad sides of the rectangular feed wave guide |80. In order that the branch wave guides |15, |16 and |11 may transmit energy without occupying too great a portion of the wall of the wave guide |80, the cylindrical wave guides may be lled with a dielectric material such as polystyrene lor paraffin or polythena The phase reversal is provided by means of artwisted septum or partition |82, which is given a quarter twist. The polarization of the oscillations in the cylindrical guide will follow the twist imposed by the septum. The twist is made in the opposite direction in alternate branch wave guides, so that in the wave guides |15 and |11 it is in one direction and in the wave guide |16 it is in the opposite direction. Thus between the ends of the wave guides `|165 and |11 there is provided a 180 phase shift as a result of the oppositely carried-out 90Y twist. This cooperates with the phase shift produced by the length of the guide |80 between the guides |16 and -|11,

which is usually in the general neighborhood of 180, say somewhere between 140 and 220, to

provide a desirable type of antenna directive. characteristic as elsewhere fully described hereof particular utility at very short wave lengths,

such as 1 cm., at which other types of construc- A tion might involve too much fine work.

One particularly useful form of apparatus ernploying the type of organization just described is shown in Fig. 9 and described below.

In order to simplify the illustration, no means were shown in Figs. 1 and 1A for varyingthe phasing of the radiating elements. An important feature of the invention lies in the fact that the phasing of the radiating elements of an antenna system in accordance with the present invention may be readily varied either continuously or intermittently without altering the frequency of operation or the relative physical location of the' said radiating elements. This important feature of the invention arises out of the fact that the radiating elements are fed from a wave guide in which the velocity of phase propagation (hence the wave length for a given frequency) may be varied. In contrast to the variation of the frequency of operation, which is very diicult because high-power generators of very high frequencies such as high-power magnetrons are extremely difficult to manufacture in tunable form and because variation of the frequency of operation would require tuning of the receiverl of the system as well as of the transmitter, it is found in connection with this invention that the variation of the velocity of phase propagation in a hollow pipe wave guide may be made both electrically and mechanically practical and simple.

Fig. 2 shows in cross section a hollow pipe Wave guide adapted for varying the wave length of oscillations at a given frequency within the wave guide, together with one of the dipoles driven by the hollow pipe wave guide and its associated feeding and supporting structure. In Fig. 2 the power distributing wave guide is formed of a channel-shaped structure 20 constituting three walls of the wave guide and a plunger member 2| forming the fourth wall of the wave guide, the wave guide being generally indicated at 22. The plunger 2| is adapted to slide up and down within the channel member 20 thus varying the broader cross-sectional dimension of the wave guide 22 and consequently varying the waver length of oscillations in the wave guide in accordance with the relation t resonant cavity may be formed along each of the corner edges of the wave guide 22 formed by the channels and 26 have adepth of anelectrical quarterfwave length'fand the distance between the mouth ofthe branch channels to the-wave guide corner where the clearance spacesg-S and 24 connect with the wave guide 2 2 is likewise an electrical quarter-wave length. The channels; 2,5 and 26 being short-circuitedat their closedends,

a low impedance will be presented at Vthe wave guide corner. Moreover, rsubstantially'no voltage will occur between the plugvstructure 2| and the channel structure v2i) where these two structuresl arein contact, Ysothat contact losses are kept at a minimum.

The form of dipole' shown incross section in Fig, 2, together with its associated feeding and.. v supporting structure is particularly well adapted for the construction of antenna systems in accordance with the present inventionj. Thefdipole `and its associated supporting structure' is illustrated in a perspective view in Fig. 2A. yThe dipole arms 28 and 29 are both supported on `a tubular member 30 which is providedrwith two ,longitudinal slots 3| and 32 at approximately 90 around the circumference of the tubular mem- `ber 3Q from the positions of the dipole arm-s 28 and 29. The outer end of the tubular member 3D is closed by a plug 34 which supports a coaxial in ner tubular member 35. The tubular member 35 is connected directly with the dipole arm 23 by means of a pin 3'5 which in addition to providing the aforesaid electrical connection also lfurnishes additional support for the tubular member 35. A rod 31 is tightly but slid'ably fitted into the tubular member 35 s-o as to project beyond its inner end and beyond the end of the Y tubular member 30 into the wave guide 22. Y

The plug 35 also closes oil the outer end of the slots 3| and 32. These slots each have a Vtotal lengthof substantially an electrical half-wave length, so that the tubular member 3|) is eiectively divided into upper and lower segments the central portions of which may be excited so that a radio-frequency voltage appears between them. Such excitation is provided by energy picked up by the rod `:il where it projects into the wave guide 22 and impressed uponl one segment of the resonant portion of the tubular structure Si! through the pin 35. The radiorequency is then fed to the dipole 28, 29 which thereupon radiates the energy. The intensityv of the excitation of any particui-ar dipole (in eiiect, the tightness or looseness with which the dipole is coupled to the :wave guide 22) may be adjusted by varying the longitudinalposition of the rod 3?.

"Ifhe various individual dipoles may be thus ad- Vguideoi variable width such as that ShOWn in Fig. 2 may 'be arranged for continuous variationfof the orientation' of the directional-maximuin'of the antenna' system. With an-arrangement similar to that of Fig. 2 the direction-al 'maximum o'f the antenna characteristic may be dimensions-ofi'-the'wave guide to the critical dimensions for the frequency iii-*question orl undesirably close` to "suchY critical `'olimension-and -in the other direction by the 'fact that widen-ing nof thevw'ave. guide 2'2by'raising theplungergZjl beyond `a Icertain amount vintroduces -thepossibility-of an-undesired! multiplicity of 'modes-of oscillation. inthe wave guide. z Moreover.zthe resonators23," 25 and 24,'2S;`1"sinceftheyaoperate n in'the`TE1,b-`mode,"are somewhat sensitivefat'o changesinthe electrical dimensions .of thewave yguide`22 'fandwill' furnish the desired apparent short circuit'atuthe co'rners'of'theiwaveV guide 'guide E0 is formed bythe plunger indi'catedlol7 dotted lines atl 52, which corresponds with the Vplunger 2| of Fig. 2. The plunger 42 is'actuated 'by a number of toggle linksl' suspended fromaI framell and'operated together by a rod 4T',so

that "the "plunger d2 'is moved vertically andremains parallel 4tofthevbo-tt'om oi the waveguide et. Themain body ofthe wave 'guide-4U is ixed tov the frame 4 6 at its outer. extremity.- A

suitable restraining guide or "bearing surfacerm'ot shown) is provided .toprevent the plunger'42 from moving longitudinally whenthe toggles are actuated. `The`rod 41 is reciprocated longituinally'by'th'e motor 48 acting through the crank 5 andthe link 5d'. The motor is preferably caused to vrevolve relatively slowly, such as at a rate'of one revolution every few seconds. Theacf tuating mechanism for the toggles 4 5 spreferably Aso arranged sothat in one'revolution of the cranl; 4S the toggles are iirstpull-ed to one side, then returned to center andfthenpushed to the other side and then again returned to center, so that four complete sweeps, two in each direction, are; accomplished for each revolution of. the motorf 'When the driving mechanism for the toggles is operated asaforesaid the' characteristic motion of the toggles' cooperates with the' type of reciprocating motion'furnished by vthe' crank i9 and the link 5e to 'provide va desirable sweep characteristic.l 1 Y U l The transmitter and receiver of the system and their associated apparatus are indicated in a general way on Fig. 3 Yby the boxes 5| and 52.' vIt Yis to be understood that the motor 43er the scanning mechanism should be connected, eithereleotrioally or mechanically, withwsomne kind Y'of device (not. shown) for furnishing to the receiver an indication of the instantaneous orientation'of the antenna system directional characteristic' in order that this `information maybe correlated with other information obtained from received signals. Apparatus of the type here shown is of particular utility in connection withradiof-fecho location and detection apparatus f which""is adapted i@ .transmit shortfdureiifrf hhegy pulses "of high-frequency"oscillation and to 'up-echoes oisuch pulses during the intervals between'p'ulses i The apparatus of Fig. Swithout further coop- Verating elements is adapted to concentratevthe radiation and the reception sensitivity of the an- 'tennasystem only in a cone which has the axis of Vthe"wavefguide f4!) for its axis and which'passes over into a plane perpendicular to the axis of the fwave guide 4!) when the'dipoles are all operatlng Vin phase. Aspreviously pointed out, some concentration oi" the vsheet of radiation isr produced and in the case of'dlpoles transverse to the Taxis o? thearray'the 'portion of the beam in which lintensity"exceeds the half-power level is concentrated' Bv uw fact fmt the nearer wall of the wavie guide Ml parallel to the dipoles acts as a wreflector, into an angle of 60 about theaxis of the? wave guide; "Further concentration of `-fthe beam may be obtained by vtheuse of an auxiliary mirror'as shown in Fig. 4, or by means illustrated vl'in'.Figs. 19 and 20, or` by both' means together. "`B`y arrangementsincluding a mirror of the type "shown in Fig. 4 afbeam mayreadily be concentrated into the form of a relatively thin pencil.

r`.if desired, the concentration in the `beam by 'meansofr the auxiliary mirror may be carried'to scm'e intermediate degree, so that the beam may be extremely narrow in one plane, such as for in- `-fstance one-.half degree wide between half-power fpoints' in a plane passing' through the axis of the dipole array, and moderately wide in another plane, possibly l0, or 20 degrees between halfpowerpoints.' Such beams are especially useful Yforfast high-resolution scanning for radio-echo flo'cationequipment. It can be shown that scany"ning with` a single pencil" beam involves Vcertain .'limits'onzthe combination of'speed and resolution, the-scanning speed permissible going vdown -with 'the narrowing of the pencil beam for a given If a pair of beams is used, each of which is nar- 'row in one dimension only and broad in the other cross-sectional dimension, and these beams are fcrossedf which is to say that one has its narro-w dimension approximately Vperpendicularv to the narrowdimension of the other beam, and Vthese beamsare then each scanned in a direction parallel'to the narrow dimension, a satisfactory high `resolution'and long range scan can-be obtained :at relatively high speed;

Ii' the area to be scanned'isnot unreasonably large, such as from ten degrees square to thirty or fortyV degrees square', the loss of gain bythe fanning 4of the .beam is not excessive, especially in viewrof the fact that the narrowing of the beam in one dimension increases the antenna system gain.

Thus, for a high-speed high-precision locating .devicetwo systems -of the type-shown in Fig. 4

Would-be used, one mounted in the general way showninFig. 4 with the axis of the dipole array approximately horizontal, and the other mounted witlithe axis of the dipole array approximately Vvertical. I f desired, Ythe entire system including the two perpendicular antenna systems could be `mounted so-that it could be swung to scan any particular restricted solid angle. This type of apparatus is of particular importance at the very short wave lengths, such as wave lengths of sev- 12 eral centimeters, where high resolution arrays are readily obtainable. in a small space, but reliable and iastscanning methods for such high resolution apparatus have heretofore been difficultto construct.r y Y In Fig. 4 the distributing wave guide isfshown at 55 and the dipoles are located at- 56. i The motor 5'! drives a toggle mechanism 58 to vary the orientation of the directional characteristics of the system in the same manner as was accomplished Vin the apparatus of Fig. 3. v'I'he dipoles 56 or, more accurately, the midline between the line of centers of the dipoles and the reflecting surface of the wave -guide`55, is located at the focal axis of a semiparabolic cylinder 59. The semiparabolic cylinder59gis a reflector, preferably made of sheet copper lor aluminum, suitably supported. The wave guidek 55 andv the dipoles 56 are inclined upward so that the maximum illumination of the reflector occurs near .the center of the semiparabolic section of thereflector instead of near the vertex, whichis in this case at or near the edge. In an apparatus ari: ranged in this manner the amount of radiation blocked ofi by the wave guide 55, the motor 5l and the associated apparatus for energizing, and so on, is kept to a practical minimum.

An antenna system of the type shown inFig. 4 including a linear wave-guide-ied radiating array and an auxiliary reflector has a particular advantage in that the frequency-sensitivity with respect to the spacing between the antenna array and the auxiliary reector is very low, if it exists at all. This is for the reason that such energy as is reflected from the auxiliary reiiector back to the antenna array when the radiated beam is radiated at an oblique angle to the axis of the arrayY will not .cause the formation-of standing waves in the wave guide system because the direction of the radiation so reiiected back to theantenna array is such as to set up a wave travelling towards the absorber M (see Fig.` 3)

A and not a wave travelling back towards the input to the antenna system. This benecial effect does not take place when the beam is at right angles to the axis of the antenna array but, as pointed out below, when the beam is so directed there will normally be a high standing-wave ratio in the wave guide for other reasons, so that the additional diiiiculty is relatively immaterial.

Fig. 5 shows another form of reilector which may be used instead of the reflector 59 for concentrating the radiated beam in a plane perpendicular to the axis of the wave guide. This form of reiiector may be referred to as a cylindrical zone plate. rlhe 4curved surfaces are segments of confocal cylindrical parabolas havingdirectrix planes separated from each other by one wave length. A study of this type of reflector has shown that the directional pattern producedby means of such a reiiector may be expected to be almost as desirable from the point of view of directivity as that obtained with an ordinary parabolic cylinder, but thatsome lowering of the gain for a given aperture is to be expected. The reflector shown in Fig. 5 is symmetrical about a plane passing through the focal axis and the lines of vertices of the Various parabolic cylindrical surfaces. If desired, this type of reflector might be modied in accordance with the principles explained in connection with Fig. 4 to make it unsymmetrical with respect to this plane so that apparatus located near the focus will not substantially block oil" the radiation.

Fig. 6 illustrates a method of altering the wave guide in order to vary the orientation of the directive pattern of the antenna system, which method may be used instead of the method shown in Fig. 2. In Fig. 6 the distributing wave guideris shown at 60. The dipoles are shown at 6|, the apparatus being shown in a position such that the dipoles are below the wave guide BS, in order that the arrangements on the back side of the wave guide 50 may conveniently be f shown. The end of the wave guide 60 is filled with absorbing material 62 corresponding to that shown at t in Fig. 3 and at I2 in Fig. 1. A series of longitudinal slots 63 is cut in the middle 'of the broad side of vthe wave guide 60 which is shown uppermost in Fig. 6, the slots preferably being made in the portions of the wave guide BD which lie between successive dipoles 6|. These slots 63, if not excessively wide, will cause substantially no interference with the normal mode of operation of the Wave guide 60 because they offer practically no interruption to any current flowing in the wave guide surfaces. A plate'64 of polystyrene or other suitable dielectric material cut in such a manner as to provide tongues adapted to be inserted through the slots 63 into the wave guide 60, is mounted, byfmeans not vshown in the drawing, so that the said tongues maybe reciprocated in and out of the wave guide Sllthrough the slots S3. In such reciprocation it is not necessary that the plate 64 be wholly withdrawn. If it is desired wholly to withdraw theV plate 64 from the wave guide 50, the slot 63 might be provided with a suitable guide. Indeed the provision of a small metal sleeve on the outer side of the slotted wall of the wave guide extending around the dielectric tongue for a small `distance away from the wave guide may serve tofmitigate radiation from the slot in cases where the slot'is wide enough to permit radiation in the absence of such sleeve.

i It will be seen that the dielectric material Yof the plate 64 is thus introduced into portions of Vthe wave guide S which have oscillating electric fields o f relatively high intensity when the wave vguide 60 is excited, so that the eiect ofl the said dielectric material upon the characteristics of the wavey guide will be quite marked. Y'I'he'said effect will be to shorten the wave length of the oscillations in the guide for a given frequency and the said wave length -will be progressively 'shorter as the amount of dielectric material introduced into the wave guide is increased. The advantage of this' method of variation of the electrical length of the wave guide 60 lies in the avoidance of discontinuities in the wave guide walls at locations of high current density. The

pedance relations, so that reiiections will be set up on account of such mismatch. VSuch reections will be at a maximum when the dipoles are 1/2 wave length apart (referring -to the wave length in the guide) but the total reflections set up diminish as .the electrical length of the guide is varied away from that corresponding to half-Wave spacing, and this decrease is particularly sharp for long arrays. In general, the portion of the scanning cycle produced'by varying the electrical length of the Wave guide in which portion a high standingwave ratio occurs will be limited to substantially one-half the beam-width, located symmetrically with respect to the half-Wave position, which is the position at which the beam is perpendicular to the axis of the wave-guide. As the array is lengthened the beam becomes sharper and the portion of the scan at which high amplitude standing waves occur becomes narrower. At the same time, however, the maximum intensity of standing Waves decreases' rather than increases with increase ofthe array length. This is due,V

at least in part, to the fact that for longer arrays the penetration of .the coupling probe into the feed wave guide will generally be less, which results in the capacitive eiect of the probes being more completely counterbalanced by the inductive'eifect of the holes in the wave guide wall through which the probes protrude. In 'addition, whenthe probe penetration is small and the array long, the attenuation in the feed wave guide becomes relatively more important and further prevents the building up of large standing wave amplitudes even for conditions of normal beams direction (the reflections from the more distant probes adding little because of attenuation).

It is possible to provide means to indicate the presence of a relatively high level of standing waves and such means may be used in connection with antenna systems herein described for the purpose of making an accurate indication of the time when Ythe beam islocated perpendicularly to the axis of the wave guide, thus providing a monitoring calibration for the means f ydiscontinuities caused :by the dielectric insertions in the wave guide in the apparatus of Fig. 6 have the same spaciall periodicity of distribution, the reflection eiects from both sources will have their disturbing influence for the same electrical length of the wave guide 60, so that these reection effects do not Vprecisely constitute an additional disadvantage of the type of arrangementsV shown in Fig. 6. Indeed it might be possible to cause'the two reilection eiects to cancel each other in part (only for some positions of the scanner, however, in the general case) In the type of apparatus shown in Fig. 6 however, it may be more difcult to keep the standing wave peaks at a reasonablylow level, especially for long arrays.

'The above-mentioned possibility of checking the orientation ofthe beam by determining the precise moment during the scanning cycle when a relatively high standing-wave ratio appears in the wave guide feeding the antenna array is of great practical significance and is applicable generally to many forms of the invention, including those of Figs. 2, 3, and 4, Fig. 7, Fig. 8, and also Fig. 1A; Apparatus for ,such'che'cking purposes is indicated in a general way in Fig. 15. The standing-waveratio'measurement is adapted to give an indication/of 'the moment when-the l lbeam is oriented perpendicularlyl to the axis of the, feed wave guide, which indication is independent of the effects of temperaturaChanges-in freferent electrical lengths of the feed wave guide l is governed by the same mathematical relations asthe intensity ofthe radiation in different directions under Vconditions of normal beam transmission (except for a factorof- 2 which comes in because the standing waves are waves which have travelled down and back in the array), the presentation ofthe standing wave ratio as a function of scanner position on a suitable oscilloscope, as just'suggested, may serve to monitor the directional-pattern ofthe antenna array. Damage to the antenna by way of -physical deformation or the like which would cause the directional pattern to deteriorate will cause a corresponding change on the indication of lthe standing wave ratio. v

The chief disadvantage of the suddenly increased standing-Wave ratio which accompanies the production of a beam normal to the axis of `the array is the possibility that the change in the load offered by the antenna resulting from the standing waves may cause the transmitting tube to shift its frequency of operation. This is of` no practical consequence for standing-wave ratios of the order of magnitude encountered in arrays Vof 50 wave lengths or longer, so far as radio-echo detection apparatus of ordinary types is concerned', but it may have some significance in the case of specialized equipment of veryhigh accuracy, such as equipment employed for directing anti-aircraft fire.. The effect of the variation in standing-wave ratio in the neighborhood of the-normal beam position of the scanner may be greatly reduced `by employingV means for varying the length of thewave guide between the feed wave guide of the antenna and the transmitting tube. Suchl means may be a section of wave guide of `variable width. The electrical length of this variable portion. of transmission means may then be adjusted so that the standing waves caused by the vscanning of the antenna through the normal beam position have a minimum effect upon the frequency of operation of the transmitter. The variable portion of wave guide thus has the function of adjusting the electrical length of the wave guide so that vthe standing waves are presented to the `transmitter tube in the most favorable phase. The de- Y sired adjustment for this. purpose may be made said structures consists of the plate 68 and the `ange structure 69, which mayV conveniently be soldered together, and the other of said structures consists of the plate i and the flange lstructure Ti, which may likewise be soldered tol and 2li; 26 of Fig. 2. In order that the discontinuity in the wave guide walls should noi-I appear .at the Wave guide corners, where circulating .so that the current flowing at such locations will be substantially less than the current flowing'at the corner. In this manner the range of wave guide width (referring to the width of the wave guide 65') vfor which the resonators 'l2 and i3 are able to give satisfactory service is extended.

The provision of means for providing the desired relative movement of the structures 68, 69, andA 10, 'll will be readily understood without further explanation. It will be seen that such means should include some arrangement for holding the two structures together, in cooperation with which the ball .bearings E7 may serve as aligning means.

The practical scope of varying the directivity of an antenna array by varying the width of a Wave guide feeding the elements .of the said Varray is illustrated in Fig. 14. Fig. 14 is a diagram showing contours of equal beam angle referred to the plane perpendicular to the` axis of the array, for different values of spacingbetween the elements of the array and for different Values of the Width of the feed wave guide in terms of the free-space wave length. The ratio of antenna element spacing to the free-space wavelength is plotted as the ordinate, and the ratio of thev widthof the wave guide, sometimes referred to as a, to the free-space wave length is plottedv as the abscissa. It is assumed that alternate antennafelements are provided with means for accomplishing a phase reversal as previously described.

The shaded area of the diagram indicates values of spacing and Width which are unsuitable for some reason or other.

Thus wave guide widths less than 0.5i are unsuitable because such wave guides are in the cut-off range, which `is to say that they will not transmit waves of the frequency in question. Wave guide widths greater than A are undesirable because of the likelihood of interference of the 'IEac modeA of transmission. The other two boundariesof the usefu1 area.are determined .by the appearance of additional beams correspondmg to an fend nre operation of the antenna array. Thus the line .A indicates the lowest spacing and guide Width required for end re operation in one direction, which maybe said to correspond to a beam of the -iorder,l the principal beam being of the order -i-1/2. Likewise, the line B indicates the greatest wave guide width for which an end-fire beam Will be produced in the opposite direction, which may be said to be a beam of -1/2 order.

The nomenclature just used for referring to the various orders of beams that may exist for various spacing and wave lengths relations will be understood by reference to the formula for the angle by which the direction of maximum emitted or received radiation deviates from the normal-direction to the array, which angle is referredto as 9:

, -Sm 6 g. s

In 'this formula A is the free space wave length, kg 4is the wave length in the feed wave guide, and s is the spacing .between elements of the array. In the case of an array of non-reversed dipoles n may take the values of 0, i-l, i2, and. so on. In the Vcase of a reversed dipole array constructed in 'accordance with the present invention, n is found tojtake the values of il/g, r3/2 and so on. The beam which isutilized in the type of scanningnormally chosen in accordance with the information shownon Fig. 14 is. that for which the, above equation holdswhen n has a value Of-ll/znf.. .Y

l;It,will be seenfrom Fig. 14 that the variation of the beam angle ,with wave guide Width is not a linear relation and that the beam angle is quite sensitive to changes in wave guide width as `the latter approaches the cut-off dimension (for which situation the wave length in the guide is innite and the velocity of phase propagation is zero). Thus, for spacing between antenna lements of approximately 0.6v free-space wave lengths, a variation in beam orientation of about 25 or 30 degrees can be practically obtained. For-the spacing yof 0.5 free-space wave lengths and less it appears from Fig. 14 that it is not practical to jinclude a .beam normal to the axis of the array within the eld of scan.. For this reason a spacing of about 0.6 is usually preferred because the inclusion of the normal orientation. within the scanning angle has the advantage of providing a calibration check through the occurrence of high-amplitude standing-waves for normal. orientation. g

I f it isY desired to make the angular rate of scan approximately linear a suitable cam or eccentric may be included in the mechanical motion which shifts the plate 'I0 with respect to the plate'63 (Fig. 7).

'Ihecross-sectional dimensions of the feed wave guide perpendicular to the variable dimension used forscanning is not particularly critical. It should be less than half of the free-space wave length in order to prevent interference with other modes and is preferably considerably shorter than such half-wave length. About 0.3 free-space wave lengths is a convenient size. The dimensions, particularly the cross-sectional length, of the channels-1,2 and 13 `are quite important. For relatively long guides the following dimensions have been found to be suitable, referring to the dimensions indicated by reference characters on Fig. '7.

xifree-space wave length One of the dipoles of the array driven by the Wave guide 66 is shown in Fig. 7 at 16. The arrangement shown in Fig. 7 for energizing the dipole v'I6 is a simplification of the energizing means shown in Fig. 2. In Fig. 7 the forward extension of vthe tubular member on which the dipole arms are mounted, which was shown in Fig. 2, has been in eifect cut-off. The slots cut in the tubular member, one of which slots appears in Fig. 7 at 11 cut in the tubular member 18, are

therefore open at their outer endsland are only about an electrical quarter-wave length long. The tubular member is thus supported wholly by the structure -19 which connects it electrically to the upper segment of the tubular member 18. The rod 8i is rmly but slidably mounted in the tubular member 80 and its longitudinal position is adapted tobe varied in order to adjust the degree of excitation of the dipole 16 relative to that of the other dipoles of the array. The type of dipole shownin Fig. 7 is somewhat more compact and slightly simpler in construction than the form shown in Fig. 2. l

As previously indicated, the angles through which thedirection of maximum eiectiveness of the antenna system may be swung by varying the lateral dimension of the distributing wave guide is subject to a practical limitation whichmakes it advisable to limit said swing to about 30 in the forms of the invention heretofore considered, especially those of Fig.2 and Fig. 7. Fig. 8 illustrates an arrangement of apparatus by which it is possible' to double the angle through which the beam can be "swung by varying the electrical length of the wave guide in any given manner. Ihe orientation of the directive pattern of the antenna system fed by a distributing wave guide in the manner above vexplained depends not only upon the electrical length of the wave guide but also upon the direction of the now of energy through the wave guide. For a given adjustment of the electrical length of the distributing wave guide at a given frequency, if when the wave guide is excited at one end the direction of maximum effectivenessof the antenna system forms an angle 0 with the'planeperpendicular to the axis of the distributing `wave guide, when the distributing wave guide is fed from the opposite end the orientation of the said direction of maximum effectiveness will be in a direction forming an angle equal to 20 with the previously obtained direction of maximum effectiveness and likewise at an angle of 0 with the plane perpendicular to the axis of the wave guide. Consequently if the wave guide can be'alternately fed from one end and then from' the other and the electrical length is varied with each type of feed from an electrical length adapted to produce radiation perpendicular to the axis of the wave guide to some other electrical length, for which the direction of maximum radiation might be displaced as much as 30 from the plane perpendicular to the'axis of the wave guide, the direction of maximum effectiveness of the antenna system can be made to swing first on one side of the broad side direction and then on the other. With such an arrangement it is quite practical to obtain a swing of 60. In Fig. 8 an arrangement is shown for exciting the wave guide alternately from each end. The wave guide 85 feeds an array of dipole antennas in the general manner heretofore explained Vand means are provided, which are not shown in Fig.` 8, for varying the electrical length of the wave guide 85 in order to vary the directional properties of the antenna system. The straight wave guide- 85 which supports the antenna array is coupled at each end with a bent wave guide (shown respectively at 86 and 86a) leading to a reversing switch 81. The reversing switch 81 may take any of a number o f forms. It may generally be referred to as a wave guide transposition switch.

The form of switch shown in Fig. 8 consists simply of a resonant ring pivotally mounted in a Y wave guide crossing.- A simple crossing is formed by the wave guide 88 and 86, 86a, the wave guide 19 88 extendingbeyond the crossing to an absorber 89. The switch -81 Vincludes a yresonant ring 81a, which is'shown .end-oniin. Fig. ,8 andwhich'is pivoted Von arr-axisperpendicular to both -wave guides.' (perpendicular to 'the 'planeof Fig.Y 8) located .substantially at Vthe center-cf .the crossing. The rescnant'rin'g B-l'c may be round'or rectangular. (orfit may have some' other shape, vorgindeed aresonant structure in some'othershape, which is :not a ring at all,y may be used), `but in the rectangular :wave guide system-.shownit isconvenient tc provide a resonant ring' of-recta'ngular form also. The dimensions of the' ring should be such astoV resonate at the frequency of -op eration and may-be designed so to vresonate' in accordancev with known' principles. z Such' a -resonant ring-acts as a-reflector of energy at such frequency.' Thusv when,- the ring 01a isoriented as'shown inFg. 8, 4communication is established for transfer of energy betweenfthe wave guide 08 and the waveguide-86 `andalsofbetweenthe Wave guidea and the 'absorber ,Br If the resonant'ring should berotated 90?, venergy--trans err'ing relation' wouldV be established betweenthe wave guides 88 and 06a andrbetweenthewave guide I'and the absorber-89'. 'Carefshould preferably vbe taken in' yoperating the-resonant ring 31a. -that the turning: motion carries the ringA through the position in which the plane of the ring vis aligned withthe direction of the-wave guide 88 and not throughi the position in Uwhich theplane of the ring is at right angles tofthe direction ofthe waveguide 8'8. If this `precautiony is taken, the intermediate position of the ring 81 :will couplethe wave' guidexSS' atleast in n filled with materialY adapted to -absorb oscillatory electric energy, corresponding in functionzto the absorbing material62 or it may takeother forms, such as a'device constructed'in accordance with the principles explained in W. `Salisburys patent application, Serial No. 486,608, which issued asPatent'No; 2,599,944 `June 10, 1952. The waveguide 88 leads directly to a'transrnitter 90 and leadsthrough a branch guide 9I`in which. isv

interposed a protective electrical breakdown device 92,"to a receiver 03;' 'The apparatus required forproviding thedesired indication in response to received signals and for performing 'various y synchronizing. functions, with which. the present invention is not directlyconcerned,- is indicated in a general way by various rectangular enclosures.

In one Vposition of the'reversing switch 81'the transmitter will feed' energy to the'wave guide 86a which willV enter the wave guide l85 at its right-hand 4end and proceed to the left, most of it beingradiated from the various dipoles of the array and asmall'remaining amouritproceeding down the wave guide 86, back tothe switch 81 and into the-absorber 89 where it is absorbed. `When the transmitter is not operating 'and echoes of transmitted pulses energize the Yantennas of `the array, the maximum sensitivity of the antenna array will be directed in substantially the same direction as `that in which the greatest intensity of the last transmitted pulse was emitted and signals coming from such direction will excite' a wave in the wave guide 85 which will flow to the right towards the receiver v93. When. the switch S'I is in its other position in the wave guide 85 Will be energized from the left-hand end and signals coming from the approximate direction in which the major portion of the radiated pulse was radiated will excite a wave flowing to the left in the wave guide 85 which will then proceed through the wave guide 86; the switch 81, the Wave guide 88 and the wave guide 9! tothe receiver 9,3.

. For some types of apparatus an extreme vrange of variationof the scanning angle is not particularly desired and it is possible to devise apparatus for such purposes having a scanning range of about 10 or so, which apparatus may include certain simplifications that would be diflicult to incorporate into devices for scanning over wide angles. Fig. 9 illustrates one such form of apparatus for scanning over an angle of about 10. The form of construction shown in Fig. 9 is particularly convenient for operation at extremely Short wave lengths such as 1 or 2 centimeters. Fig. 9 shows a cross-section of a type of array embodying the principles illustrated in connection with Fig. 1'7 and Fig. 18. The cylindrical branch wave guides with their twisted septa are in this case fed from the narrow side of the feed Wave guide (shown at 200), in order that the width of the feed wave guide 200 may be simply varied by varying the separation between the two metal pieces 201 and 202 which form the waveguide 200. No significant amount of energy Will be dissipated through the gap between the pieces 20d and 202 which communicate with the Wave guideA 200, because this gap occursonly at the center line of each of the broad walls of the wave guide 200; across these centerv lines there is no tendency for oscillatory currents to ow. This method of varying the Width of the wave guide 200 has the advantage that it dispenses withthe necessity of providing choke resonators such as the resonators 'l2 and 13 of Fig. '7, but this convenient method is not believed to be practical for scanning which vcovers more than an angle of about 10", because considerable amounts of energy will begin to leak out of the gap between the metal pieces 20| and 202 if this gap is made wide enough to produce the variation in width necessary for the greaterrangeof angular scan.

As shown in Fig. 9, the cylindrical branch wave guides are formed in the same metal piece 20| which forms the upper portion of thev waveguide 200. One of these branch wave guides is shown in section at 203. In order to reduce the diameter of the branch Wave guide a lling of solid dielectric material such as polystyrene is provided as shown at 204. The twisted. septum, which may be of thin sheet copper, is shown at 205. The bottom of the septum 205 is parallel to the axis of the wave guide 200, whereas the top of the septum 205 is perpendicular to the said axis. The septum 205 and the two pieces of solid dielectric material 204 may be assembled beforehand (if desired the dielectric material lmay be molded about the septum in a suitable cylindrical mold) and these assemblies may be simply inserted into the cylindrical recesses of metallic piece 20! and then aligned therein for proper orientation of the septa. As mentioned in connection with Figs. 17 and v18 in alternate elements the septa are respectively twisted inopposite directions. A small hole 206 in the wall of the wave guide 200 provides 21 for energy transfer from the wave guide 200 into the cylindrical branch wave guide 203. The size of the hole 206 depends upon the number of elements in the array and the desired degree of coupling.

Variation of the width of the wave guide 200 is accomplished by the motions of a rocker arm 2|0 controlled by the cam 2 and the cam follower 2|2. The rocker arm 2|0 is pivoted at the ball bearings 2 I 4. Since the metal piece 202 need not be very heavy and since the range of its movement for a 10 scan will not be great, the type of apparatus shown in Fig. 9 lends itself very well to rapid scanning. V

Fig. l illustrates application of the principles of the present invention for providing an antenna system the directive maximum of which may be swung in two coordinates without motion of the radiating elements themselves. In this form of apparatus energy is introduced into a wave guide |00 at |0|. rIhis energy is transmitted from the wave guide |00 into a plurality of branch wave guides |02 which may be formed by suitable partitions in a metallic box-like structure through suitable windows |03 in one of the narrow walls of the wave guide |0|. The electrical length of the wave guide |00 is adapted to be `varied by movement of a lateral plunger |04. Absorbing material shown at |05 is located in the end of the wave guide |00. If desired, suitable structures having the effect of shunt susceptances may be provided in the wave guide |00 between the windows |03 in order to match out at least in part the reflections occurring in the wave guide |00 on account of the junctions effected through the windows |03.

The branch wave guides |02 are each provided with a row of dipoles in the general manner heretofore explained, the dipoles being represented in Fig. in the form shown in Fig. 7. The dipoles are mounted on a single flat surface and are distributed uniformly both in the direction of the wave guide |02 and in the direction of the wave guide |00. The spacing in each of these directions should be less than the wave length in unconned air of oscillations of the frequency intended to be transmitted or received. Accordingly, provision should be made for reversing successive arrays, either by reversing the polarity of the rst dipoles in each array, or by 0.7 free space wave lengths for the oscillations in question. The electrical length of the wave guide |02 is adapted to be varied simultaneously by the movement of plates |06 of dielectric material, such as polystyrene, having tongues |01 projecting into the wave guide |02. The plates |06 are actuated in unison by the vertical motion of a plate |08 to which the plates |06 are attached. The motion of the plate |00 may be brought about by suitable shaft eccentrics or cams, or the like (not shown) or by hydraulic or other means. Motion of the plate |08 causes the orientation of the directive characteristics of the antenna system to be swung about an axis parallel to the axis of the wave guide |00 whereas motion of plunger |04 in and out of the wave guide |00 causes the said directive characteristics to be swung about an axis parallel with the axes of the wave guides |02. Y

Preferably one of the swinging motions is made considerably slower than the other in order that a solid angle may be scanned with relatively uniform coverage. For example, the plate |08 may be caused to move Very slowly up and down while the plunger |04 operates at a higher frequency, making perhaps 20 or maybe 50 cycles of reciprocation for each Acycle of the plate |08. The sharper the beam of the antenna system, the greater number of cycles it will be necessary for the plunger |04 to make for a cycle of the plate |08 in order to obtain a reasonably complete coverage of the entire solid angle in each cycle. If desired, the plate |08 and the plunger |04 may be actuated with the same periodicity but with a phase difference in their motion of one-quarter of a cycle, in which case the beam will describe a circle or more exactly a cone. Such circular motion might, if desired, be superimposed upon another motion of the beam. Circular motions of this sort are of particular utility in automatic following apparatus.

If it is desired to employ the principle illustrated in connection with Fig. 8, to extend the scanning abilities of an apparatus such as Fig. 10, the wave guides |02, instead of being terminated by absorbing masses such as the absorbing element |09, might be terminated by another wave guide parallel to the wave guide |00 and connected to the wave guide |02 by Windows similar to the windows |03. In such case, it would be necessary to provide a selector switch which would enable feeding the antenna system in turn from each of the four corners through one of the extremities of the wave guide |00 or of the complimentary wav-e guide at the other end of the Wave guide |02, the three unused extremities being connected to absorbers.

Fig. l5 illustrates another form of antenna system according to the present invention differing in minor particulars from certain forms already described. In this case the dipoles, which appear at |40, are arranged in a collinear array instead of in a broadside array. 'I'he directive pattern is still a broadside pattern. Phase reversing arrangements are provided in alternate dipole feeds as in previous cases. The dipole mounts |4| are of the type shown in Fig. 2. The feed wave guides constituting the dipole mounts |4| are connected with a radio transmitting and `receiving system by means of a wave guide |43.

The transmitter is shown at |44 and includes a vacuum tube |45 for generating high-frequency oscillations. Circuits for causing the transmitter to operate intermittently at high energy levels are included in the box shown at |46. A branch wave guide |41 leads through a protective electrical breakdown device |48 to a receiver |49, |50, which receiver includes at least one indicator |5 which may be a cathode ray tube. The circuits of the cathode ray indicator tube are coordinated with the apparatus indicated at |46 for purposes of synchronizing the indication of information obtained by the system, such synchronization being provided through suitable connections indicated by the wire |63. A wire |52, also connected to the indicator |5|, is connected to a standing-wave detector apparatus |53, which may consist of a wave separator and a detector i 'and which is adapted to indicate the moment of maximum standing wave ratio in the wave guide |42 for the purpose of providing a reference point on the indicator |5|. Such a reference marker is a highly useful check on the operation of the system because it is independent of thermal effects on the waveguide structure, slippage in translating devices, changes in frequency of operation and other such sources of errors. The right-hand end of the Wave guide |43 is terminated with absorbing material indicated at If-i.

The wave guide |63 is variable in width through afsuitable arrangement which may be that of Fig. 7,'or that of Fig. 2, or some other similar structure. The fixed portion of the wave guide |53 carries a flange |55 upon which a motor |55 is mounted which is arranged to drive a longitudinal-shaft |51 which operates a plurality of short transverse shafts |58 which act to vary the width of the wave guide, as by the action of suitable cams located on the respective shafts |58. A translating device |60 which may be a suitable potentiometer, condenser or variable transformer (selsyn) is also mounted upon the fixed portion of the wave guide M3 and is adapted to be controlled by the mechanical motion of the wave guide width varying mechanism. The device |60 may be driven by a suitable cam on the shaft |51 or by a mechanical link to the movable wall of the Wave guide |43, such mechanical link or cam cooperating withv the electrical characteristics of the translating device to provide a suitable continuous indication of the orientation of the beam to the circuits associated with the indicator |5|, through the electrical connection indicated at ISL The motor |56, the shaft |51, and apparatus associated therewith may be conveniently mounted on .the opposite side of the wave guide structure '|63 in such a manner that the antenna array may be used with a mirror in the form of a cylindrical parabola with a, minimum of interference with the radiam tion pattern on the part of the scanning mechamsm. Y

The indication of the orientation of the beam provided to the indicator |51 and its associated circuits, instead of being provided through a mechanical arrangement and translated into electrical quantities by means of a potentiometer, a variable transformer or some other type of translating device, may be provided wholly by electrical methods by providing a phase-sensitive circuit adapted to measure electrically the change in electrical length of the Wave guide |43. For this purpose a pair of probes or other coupling elements associated with the wave guide |23, one near each end thereof, may be used in a suitable circuit. These probes may be placed either through the wall of the guide, to pick up the field inside, or outside the guide, to pick up the field radiated from the dipoles. Phase comparison between the two probes will indicate changes of electrical length less than a wave length and a, suitable counting or registering device may be provided to indicate changes in electrical length greater than a wave length. If the dipole array is long, the latter alone may be sufficient. The counting or registering device may be associated with a-reversing switch operated by the scanning mechanism so that the counting device indicates increase of electrical length during narrowing of the wave guide and decrease during broadening of the wave guide. As another possibility, abeam direction indicatingsystemincluding a mechanical arrangement such as that indicated in Fig. l5, may be used for controlling the deflecting plates or" the cathode ray tubes that may be the indicator i5 and electrical means of the Atype just mentioned may be employed to provide a series or" check points or markers on the indicator |5| corresponding to electrical lengths of the Wave guide |43 differing from each other by one wave length. A reduced number of check points, each of them 24 sharply denned, can be obtained by mixing the amount of radio-frequency energy picked up by a plural-ity of probes spaced regularly alongthe array. In cooperation with the reference marker provided by the operation of the standing wave detector |53, such check points could be used to facilitate relatively accurate reading of the information presented upon the indicator |5I.

Figs. 19 and 20 illustrate simple ways of pro-l viding a certain amount of concentrationfof 'the radiation of an array constructed in accordance with the present invention, with respect to direction in a plane perpendicular to the axis of the array. The concentration so provided is not very great but it is useful for many purposes. This type of arrangement is particularly eifective when the dipoies are oriented to form a co-linear array since in such case all portions of the dipoles are at the same distance from the areas relecting members. This type of reector can, however, b-e utilized to some extent when the dipoles are not parallel to the axis o f the feed wave guide and are therefore not co-linear.

In Fig. 19 an arrangement is shown which provides a reiiector in the form of a rectangular corner or edge, one side of the rectangular corner being formed by the plate 223, which Aalso forms the upper wall of the Wave guide ZIB and the other side of the corner is formed by the metal plate 22| which is mounted on the plate 22B. The plate 22| is preferably mounted on the plate 220 in such a manner that the dipoles will be equidistant from both the plate 22| and the plate 220.

In Fig. 20 an arrangement is shown, the view being this time a cross-section, in which two sheet metal reflectors are mounted on the wave guide wall which carries the dipole array. These reflectors may be straight or curved and may be either symmetrically or unsymmetrically arranged With respect to the dipoles, according to the type of energy distribution which is desired. In Fig. 2O the upper reflector 225 is curved and is somewhat larger than the lower'reector 226 which is nat.

In order to provide good energy transfer characteristics between the antenna arrays using a variable-width wave guide and radio-echo transmitting and receiving equipment and in order to reduce standing waves in transmitting equipment during the operation of the latter it is desirable to provide automatically variable impedancematching devices between the variable-width wave guide and the xed Wave guide which is connected to the radio transmitting and receiving equipment. The significance of such means arises from the fact that the characteristic impedance (or the parameter that corresponds thereto in a hollow-pipe wave guide) varies with the wave guide width for a given short dimension of the wave guide cross-section, at least if the Xed-width wave guide coupled to the variablewidth wave guide is not always aligned with the center of the latter. Figs. 21 and 22 illustrate an arrangement for providing a gradual taper from the iixed wave guide to the wave guide of variable width. The taper is provided by a pivoted piece of metal 23@ which forms one of the narrow sides of the end portion of the variable- Width Wave guide.

Fig. 21 is a front view, with the front plate 23|, which carries the dipoles, partly broken away. Fig. 22 is a cross-section. The upper narrow wall 232 of the feed wave guide 233 is Xed in position upon the front plate 23|. The lower narrow Wall 235 of the main portion of the wave guide 233 reciprocates uniformly in a vertical direction, as driven by the scanning mechanism, and is fastened upon a back plate 236 which partakes of the same motion. The end of the Imetal piece 23|) which is nearest the antenna array is Alower wall of the main portion of the feed wave guide 233. The left-hand end of the metal piece 230, however, will be required by the pin 24| to remain in substantially the same vertical position, the mechanical motion being taken up by a certain amount of horizontal motion at the slot 241|. This type of arrangement is therefore adapted to provide a tapering transition between the i-lxed wave guide 253 and the variable-width wave guide 233, whateverparticular width the wave guide 233 may have within the range of the scanning motion.

f lSince the metal piece 230 moves not only relative to the fixed front plate 23| but also relative to the back plate 235 upon which'it is pivoted,

it is necessary to provide the metal piece 230 with two choke resonators instead of one. These are shown at 245 and 226 respectively (see Fig. 22). In' order that both of these resonator grooves may be conveniently accommodated in the metal piece 230, they are filled-with a solid dielectric material such as polystyrene, which results in an increase of electrical length for a given physical length, so that the physical depth dimensions can be made conveniently small.

Figs. 23 and 24 illustrate an arrangementl for maintaining a desirable degree of power transfer between a wave guide of xed Width and a wave guide of variable width without the use of taper sections. This device depends uponthe discovery -v that a satisfactory impedance match can be maintained provided that the wave guide .of Afixed width is moved so that it remains centered with respect to the wave guide of variable width. Fig. 23'is a back view of one form of arrangement operating on this principle and Fig. 24 isa crosssection of the same along the line 24-24 of Figj'z. ,Y Y Y Y" The fixed front plate which carries the dipole is shown at 250. at 25|. A rack 252 is mounted on the latter and another rack 253 is mounted upon a bracket 254 which is carried on the front plate 250 near one of its longitudinal extremities. A pair of pinions 255 and 256 are arranged to engage the racks 252 and 253 and are mounted in a small frame 258. It will be seen that the movement of the rack 252 as a result of the scanning motion impressed upon the back plate` 25| will impress upon the frame 253 a motion having half the amplitude of the driving motion. This motion is then impressed upon the. fixed-width wave guide 260 by means of an arm 26| which is fastened to the wave guide 260 by means of a pivot connection.

VThe wave guide 253 is folded back on itself as partly shown at 252 in Fig. 23, the back portion'of the part of the wave guide 250 which is so folded back being broken away 'at 263 in order to simpli- The movable back plate is shown' through an angle a the antennanext to` it will ceiving circularly polarized waves.

fy the illustration. The general disposition of theV wave guide 26|) follows the arrangement of Fig. 8.. At a suitable place in the portion of wave guidethus folded'in back of the antenna array a wobble joint is provided in a well-known way in order to permit the wave guide 260 to follow the motionimpressedupon it by the frame 258. Because the motion of the frame 258 has exactly half the amplitude ofthe motion of the back plate 25|, the position of the frame 258 can be adjusted so that the wave guide 260 is automatically maintained centered with respect to the variable-width wave guide which feeds the an- .tenna array.

For antenna systems in which the range of width variation of the antenna feed wave guide is relatively small, as in the case of the apparatus of Fig. 9, it is not necessary to use either an arrangement of the type of Figs. 21 and 22 or an arrangement of the type of Figs. 23 and 24. In such case the wave guide connecting to the transmitting and receiving apparatus may be simply tapered to somesuitable average width and centered with respect to the average-width position of the variable-width wave guide or some other suitable mean position thereof.

Fig. `11 shows an antenna for radiating or re- The antenna is fed yfrom a ,coaxial transmission line compris- Ying the outer conductor ||0 and the inner contions ofconductor so folded being a quarter-wave length. Consequently, the dipole |I3 will be energized with a phase delay of with respect to the energization of the'dipole ||2. The resultant radiated wave will therefore be circularly polarized.

Figs. 12 and 1 3v show an arrangement for utilizing'antennas ofthe type shown in Fig. 11 in a system in accordance with the present invention. As shown in Fig. 12, in this arrangement antennasofthe type shown inFig. 11 are mounted upon a distributing wave guide |20 so as to be supported and energized by said wave guide but in a manner adapted to permit rotation of the antennas by thegears I2 |22 and |23 which are V.fixed to the outer conductors of the transmission lines `feeding the respective antennas.

Y Each of these gears is .driven by another gear, suchl as those shown at I 24, |25 and |25, which in turn are driven from a common source of power at suitable relative speeds. 'Ihe gear ratios are so constructed that Vwhen the gears are driven by a *common* drive there is a progressive difference in relative rate of rotation between successive antennas for the whole length of the array. Thus the middle 'antenna of the array may remain xed and the antennas on one side of the array y mayv be'arranged to rotate in one direction` with therate of rotation being suchthat when the antenna next to the fixed antenna rotates rotate throughan'an'gle V2a the next one through an angle Scand so on.` `The antennas on the other side ofthe fixed antenna will rotate in a similar manner except inthe opposite direction. If desired, instead of accomplishing the rotation .through asys'tem of gearing, itY could be ob- YelectricV tained by a system of synchronous motors.

As willb Aseen from Fig. 12 alternate antennas terial 13 1'.

in the array are reversed lwith regardto their connection to the feed line so that when the array is in what may be termed the zero position, all the vertical dipoles will be energized in phase and all of the horizontal dipoles likewise in phase, if the spacing is 180 -electrical degrees in the wave guide. The antennas are-preferably separated by lengths of the wave guide 121] measuring electrically approximately 160, although the electrical length may be varied within relatively wide limits for this purpose. An electrical spacing of 180? is to be avoided on account of the occurrence of reilections unless elaborate precautions are taken for matching the antennas to the wave guide. The general aspect of the change in the directive pattern obtained by rotating the antennas as described is the same for 160 spacing and 180 spacing but the. formulae relating lto the matter are simpler for the case of 180?. For 180 spacing the angle of the beam emitted by the array will be given by the formula i a y 1 H sin s (2T-ilo) A,

where .7c is any integer which makes@ a real angle. l represents the wave length in free space of the radiation in question, s the spacing between antenna centers and a the anglel through which the antenna next to the fixed center antenna has been rotatedfrom the position for which the radiationwas normal to the array. i.

The advantage of this type of system is that the beam may be swung without any oscillating motions. For certain anglesfhowever, two beams will exist when the spacing between antennas is more than y2. of the free space wave length, but for air-filled vguides of practical dimensions, a single beam is vemitted forja substantial portion of Ythe cycle. The apparatus may be turned ofi during other parts ofthe cycle. The introduction of solid dielectric material into the wave guide 123 may permit increase of the angle through which the beam can be swung without the" occurrence of ambiguity.

VA special type of auxiliary reflector is necessaryfor practical application of an apparatus of the type illustrated in Fig. 12. An apparatus of the type shown in Fig. 12 is not suitable for sending out pulses of energy and receiving them at the same time in the normal way because the returning waves, having beeny reflected once, will in eifect be circularly polarized in the opposite sense andthe components thereof will be cancelledin'the antenna elements instead of being reinforced, so that no waves will be produced in thev wave guide 126. could `notbe used for receiving and transmitting in` an ordinary duplex-operation system, except for the reception of echoes from double reflections. Antenna systems of this type can, however, be used in ordinary duplex-operation systems by providing a special type of auxiliary reflector as shown in Figj'l2. The vauxiliary re- A-ilector shown in Fig. 13 has the shape of a semi- Y parabolic cylinder and consists of a reflecting metallic sheet'l, a dielectric material onvthe frontl of the reflecting sheet 13) having a thickness of approximately 1/awave length :and shown at 131i, and a series of parallel wires parallel to the focal axis of the parabolic cylinder 1311 mounted onthe front face of the dielectric ma- These parallel'wires are indicated at 132.

Circularly polarized waves are radiated by an array of antennas one of which is Vshown at 135,

28 which antennas are fed by the wave guide |36 andare rotated by the spur gears 131 and 138 and by the bevel gears 13S and 139m. The bevel gear 139e is mounted on a drive shaft which provides a common drive for all the rotating antennas.v When the circularly polarized radiation reaches the parallel wires 132, the horizontal Thus the antenna system component is reflected but the vertical component proceeds through the dielectric material 131 to the sheet 1313 where it in turn is reflected and proceeds back through the dielectric material. Since the dielectric material has a thickness of 1/8 wave length, the additional path of the vertical component has an electrical length 0f a quarterwave length, so that the resultant of the reflected vertical component and the horizontal component reflected by the wires 132 will be a planepolarized wave, the plane of polarization being at an angle of 45 to the horizontal. When echoes of the same polarization are received, the auxiliary reflector 130, 131, 132 will convert the received Wave into circular polarization which is adapted to be picked up by the antennas 135 and to set up a wave in the wave guide 136 and ,this wave will travel toward the transmitter.

Such wave is then transmitted to a branch wave guide (not shown) leading to a receiver (not shown). The antennas 135 and the wave guide 13S-rare lso located that the focal axis passes between the antennas and the nearer side of the wave guide 136, so that the reflector 13D, 131, 132will act to concentrate the beam of radiation produced.

For large deviations of the radiated beam from the plane normal to the axis of the wave guide 135, the phase change of the vertical component of the. radiation in the dielectric material 131 wills-be less than the desired so that the apparatus will function less eectively. This effect will be less noticeable, the higher the dielectric constant of the dielectric material used, because of refraction of the ray from air into the dielectric medium. The phase change is reduced approximately by the factor cos 02, when 02, the angle of refraction, is small. It is precisely for the greater deviations, however, that there arises the diiculty mentioned in connection with Fig.y

12` relating to the formation of more than one beam. Thus-another reason exists in the apparatus of Fig. 13 for shutting orf the transmitter for the period during which the position of the rotatable antennas is such that the radiated beam would have an orientation at a large angle to the plane normal to the axis of the wave guide Anotherl advantage of the apparatus shown in Figs. 12 an-d13 is that the standing-wave ratio in the wave guide 1315v could be expected to remain substantially constant since the rotation of 'the antennas should have practically no effect upon the., impedance match between the antennas and the wave guide 13B.

Although the apparatus shown in Figs. 12 and 13 uses a distributing Wave guide of fixed dimen- :sions and electrica1 length, the means for rotating` the various antennas constitute in effect means for causing a progressive relative shift in v.phase between successive antennas of the array, just' as the means illustrated in connection with What is claimed is: v

1. An antenna system with a variable directional characteristic including a plurality of uniformly spaced dipoles, successivedipolesbeing separated by notV more than the free-space .wave length of waves in connection with which said system adapted to operate, a wave guide in energyetransferring relationship with said dipoles, means for varying the phase velocity in' at least portions of said wave guide, and means providing for a 18.0 phase shift of radiation from alternate dipolesin addition to 'such phase shift as arises from saidwave guide.

2. An antenna system rwith a variable directional characteristic including a i plurality. 'of regularly spaced dipoles separated by not more than the free-space .wave length otoscillations in connection with which said system is adapted to operate, a hollow, `metallic .wave guide .in

energy-transferring relation with said dipoles, .means for connecting saiddipoles with said .wave

vguidezto'complete said energy transferringrela- `tion providing for reversed connections for alter- ,nate dipoles,'and means for varying the electrical length of.; at least portions said waveguide.

.4. An antenna I 1. 3. An antenna system with a variab1e1direc- `said wave guide, said means all having substantially the same electrical length but providing reversed connections and consequent Vphase inversion for alternately located dipoles, and means for varying in the same proportionthe electrical lengthfof .the respectivey portions.V of said wave guide lying between said dipole-connecting means. v

system with a variable direc- '.tional characteristicl including a row oi uniy formly spaced dipoles arranged with their centers :substantially in a straight line and separated'by --less than the free-space wave length of oscillae '1 tions for' which the saidl system is adapted,1;a

straight, hollow, metallic vwave guide, means coupling, each of said dipoles to saidlwave guidev 1n electrical energy-transferring relation, and means all having substantially the same. electrical length but, providingV reversed connections; and consequent phase inversionfor alternate dipoles .oisaid row, and means disposed within said wave ..fguide for varying the phase velocity in at least ,portions of said wave guide adapted to vary in`r A flthecsame proportion theelectrical .length of the V respective vportions of said wave guide lying be- Vvtween said-dipole-connecting means..`

lg .5. An, antenna system with a Variable directionalfcharacteristic including a row of dipoles.

l separated by not more than the free-spacewave length of oscillations for which the said system is adapted,y a hollow wave guide adapted to trans- 'electromagnetic energy in the TEM mode ,without substantial interference from other modes, means associated with each of said d ipoles coupling said dipoles to said waveguide 1n electrical energy transferring relation, said 1 meansv all having substantially the same electrical length but providing reversed connections and Ac ionsequent phase inversion for alternately ylocatedvdipoles, and means for varying in the slameproportionthe electrical length of respec- -tvecportionspf Said WaveV guide 151mg between .fsaidfdipole-,connectinc means the coupling between the respective dipoles and the wave guide in energy transferring relation therewith. l

'7.,An antenna system with a variable directional characteristic including a straight hollow wave guide, a row of uniformly spaced dipoles supported on said wave guide, successive members of said row having their respective centers separated by less than the` free-space wave lengths of oscillations for which the said system is adapted, supporting and connecting means forl each of said dipoles for supporting said dipoles with respect to said waveguide and connecting them therewith in electrical energy transferring relation, said means all having substantially the same electrical length but those of said meansrwhich are associated with alternate dipoles of said row having reversed connections with said dipoles adapted to produce phase inversion,. and means disposedwithin said wave guide for varying in the same proportion the electrical length of the respective' portions of .said wave guide lying between successive supportingand connecting means. Y

j 8. An antenna system according to claim 7 in which the supporting and connecting means associatedwith the dipoles include a central conductor` projecting intdsaid wave guide which is adjustable in respect of-'the extent it projects Y therein.

9. An antenna system in accordance with claim 2 in which the wave guide therein specied is terminated at one `extremity by means absorbent of electricalr oscillations from said wave guide without the production of substantial reiiection.

10. An 'antenna system including. a row ,ofY dipoles mounted on a wave guide at a distance of approximately a'vquarter-wave length fromk the outer surface thereof and connected electrically to said waveguide by means of connecting means, the connections of which are reversed in the case of alternate dipoles of said row, the centers of Vsaid dipoles b eing spaced by less than the freespacewave `length of oscillations for which said antenna system is adaptedrmeans for varying the electrical length of said wave guide,.a reflector having theshape of a portion of a parabolic cylinder located withits focal axis parallel .to the axisof said waveguide and lying between Asaid wave guide and said row of dipoles, said reflector being. -further oriented so that the direction of maximum .radiation of said dipoles in a plane perpendicular to the axis of saidwave guide is directed approximately toward the central part of the intersection ofv such plane with Y the saidreflector.v

l1. An antenna system according to claim 3 in which the means.. for varying the electrical length. of portions of said wave guide comprises y tongues'o'f dielectric material protruding through centrally located longitudinal slots ina wall of A' in said slots.`

said wave guilde and into said vwave guide together. with'emeans for simultaneously reciprocably `moving said tongues of dielectric material 12. An antenna system including a substanftially rectangular wave guide of variable width formed of two laterally shiftable portions, said portions each including Va plate and a ange structurasaid flange structure being shaped to include ,a corner of the said Wave guide and being 'further provided with Va groove adapted to cooperate with; clearance betweenk the said `por- 

